Yeah I noticed the AI suck too, but I had a lot of bad games before finally winning that one, just as a human. Some games I could even could tell I had great starts in but just never got any kind of strength to compete with the cheating Endless difficulty. Usually a very good start as a handful of the races for me is almost a guaranteed victory, especially if I allow myself to become a part of one of the big alliances that is super-likely to form. Every game I try Hissho I just feel like, as another race, I'd have stronger military, or stronger industry, or stronger science, or whatever else. I never feel like I have a strength as that faction.
As for Umbral Choir, they are the reason I have to re-disable economic victory, because for some reason they build just massively stupid amounts of dust, and the AI very clearly can't seem to take the steps necessary to find sanctuaries and destroy them at war. Basically UC just gets to sit comfy all game and play SimCity.